The present invention relates to a bulb for a color cathode ray tube and a color cathode ray tube, and also relates to methods for the production thereof.
For example, in a bulb for a color cathode ray tube having a color selection member of aperture grille type, generally, an inner surface of a face plate has, for example, stripe-shaped fluorescent material layers for red, green and blue and a black-matrix (stripe-shaped light absorption black layer) present between one of the fluorescent material layers and another. And, an electron gun is incorporated into the above bulb, and the inside of the bulb is vacuumed, whereby a color cathode ray tube is completed. The method of forming the above stripe-shaped color fluorescent layer will be explained with reference to schematic partial end views of the face plate, etc., shown in FIGS. 47A to 47C and FIGS. 48A and 48B. The above stripe-shaped color fluorescent layer is formed by means of an opening portion, more specifically, by means of a face plate 11 to which a color selection member 13 of aperture grille type having stripe-shaped slits 14 extending in parallel with the perpendicular direction of the face plate 11 is attached. FIG. 47B alone shows the color selection member 13.
First, a light sensitive film 20 is applied to the inner surface of the face plate 11 and dried (see FIG. 47A), and then, a stripe-shaped exposed region 21 is formed in the light sensitive film 20 with an ultraviolet light which is emitted from an exposure light source (not shown) and passes through the stripe-shaped slit 14 formed in the color selection member 13 (see FIG. 47B). For forming fluorescent material layers for red, green and blue, the above exposure is carried out three times by changing the exposure light source in position for each time. Then, the light sensitive film 20 is developed and selectively removed, to retain a remaining portion (exposed and developed light sensitive film) 22 on the inner surface of the face plate 11 (see FIG. 47C). Then, a carbon agent is applied to the entire surface, and the remaining portion 22 of the light sensitive film and the carbon agent thereon are removed by a lift-off method, to form a stripe-shaped black-matrix 23 composed of the carbon agent (see FIG. 48A). Then, fluorescent material layers 24 for red, green and blue are formed on the exposed inner surfaces of the face plate (portion 11B of exposed inner surface of the face plate 11, the portion 11B being present between one black-matrix 23 and another black-matrix 23) (see FIG. 48B). Specifically, for example, a photosensitive fluorescent material slurry for red is applied to the entire surface, exposed to a light and developed, then, a photosensitive fluorescent material slurry for green is applied to the entire surface, exposed to a light and developed, and further, a photosensitive fluorescent material slurry for blue is applied, exposed to a light and developed.
In the above exposure method, an ultraviolet light emitted from one exposure light source is used. In some optical dimensions of a bulb for a color cathode ray tube, an exposure intensity of a transmitted light (exposure dosage on the light sensitive film 20) of an ultraviolet light through the slit 14 which is an opening portion formed in the color selection member 13, has a distribution of a Fresnel diffraction wave as is schematically shown in FIG. 52A. The above Fresnel diffraction is known as near-field diffraction, and generally is obtained when an observation screen is located in a finite distance from a diffraction aperture. In the graph of the exposure intensity of the transmitted light in FIG. 52A, the axis of abscissas shows the horizontal direction of the face plate and the axis of ordinates show the exposure intensity of the transmitted light. Further, the origin is the center of the stripe-shaped exposed region of the light sensitive film.
When the above light sensitive film 20 is exposed to a light, developed and selectively removed, heavy convexo-concave shapes are formed in edge portions of the remaining portion 22 of the light sensitive film (see FIG. 52B). The above phenomenon is caused by the formation of stripe-shaped edge portions of the exposed region 21 on the basis of an area of a transmitted-light strength in which area the derivative of the first order (∂I/∂x) of the transmitted-light strength on the light sensitive film 20 has an extremely small value. In the above expression, xe2x80x9cIxe2x80x9d stands for a transmitted-light intensity (in other words, exposure dosage on the light sensitive film 20) and xe2x80x9cxxe2x80x9d stands for an electron beam sweep direction, specifically, the horizontal direction of the face plate 11. If the derivative of the first order (∂I/∂x) of the transmitted-light strength on the light sensitive film 20 comes to be an extremely small value, the value of the derivative of the first order of crosslinking degree distribution of the light sensitive film 20 comes to be small (that is, the crosslinking degree distribution of the light sensitive film 20 in the horizontal direction of the face plate 11 loses steepness), so that the heavy convexo-concave shapes are formed in the edge portions of the remaining portion 22 of the light sensitive film. As a result, the edge portions of the stripe-shaped fluorescent material layer 24 cause heavy convexo-concave shapes, macroscopically, an image display non-uniformity is caused in a color cathode ray tube, and the color cathode ray tube is extremely deteriorated in quality.
JP-A-60-84738 discloses a method for avoiding the above phenomenon. In the method disclosed in the above Laid-Open publication, a plurality of exposure light sources are arranged in different positions along the horizontal direction of the face plate, and a light sensitive film formed on an inner surface of a face plate is exposed to a predetermined stripe width using a transmitted-light strength distribution of superposed Fresnel diffraction waves. And, a correction lens system for correcting Fresnel diffraction conditions of each is selected depending upon an exposure light in the position of each exposure light source, and a plurality of exposure lights emitted from a plurality of the exposure light sources are adjusted such that Fresnel diffraction waves are superposed on the light sensitive film through the correction lens system and the color selection member for one stripe having a predetermined width. Further, a plurality of the exposure lights are adjusted such that the transmitted-light strength distribution is nearly constant on the entire surface of the light sensitive film formed on the inner surface of the face plate, and further that exposure is effected in a state where a differential value (∂i/∂x) of the transmitted-light strength distribution on a position corresponding to the edge of the stripe width is a value near a peak of the distribution of the differential value (∂i/∂x) or a value that has a certain level sufficient for preventing an edge non-uniformity of the stripe width.
The method disclosed in the above Laid-Open publication is effective for preventing the heavy convexo-concave shapes which occur in the edges of the remaining portion of the light sensitive film. It is remarkably suitable for producing a so-called commercial color cathode ray tube in which slits of a color selection member in a central portion of a bulb for a color cathode ray tube have a rough pitch or a color cathode ray tube for a computer display in which slits have a fine pitch. However, slits of a color selection member in a central portion of a bulb for a color cathode ray tube for digital broadcasting have a semi-fine pitch, and the semi-fine pitch is in an intermediate range between the pitch of slits of the color selection member in the commercial color cathode ray tube and the pitch of slits of the color selection member in the high-resolution color cathode ray tube for the computer display.
It has been found that even if the method disclosed in JP-A-60-84738 is employed for a color cathode ray tube in which the pitch of slits of the color selection member is in an intermediate range as described above, the heavy convexo-concave shapes are formed in edges of part of the light sensitive film remaining after exposure and development. As a result, the heavy convexo-concave shapes are formed in the edge portions of the stripe-shaped fluorescent material layer, and macroscopically, image display non-uniformity is caused in part of the color cathode ray tube, so that the color cathode ray tube is downgraded in quality to a great extent.
Therefore, concerning a color cathode ray tube in which the pitch of the opening portions formed in a color selection member is in an intermediate range between the pitch of the opening portions formed in the color selection member in a commercial color cathode ray tube and the pitch of the opening portions formed in the color selection member in a high-resolution color cathode ray tube for a computer display, it is therefore an object of the present invention to provide a color cathode ray tube which permits the prevention of formation of convexo-concave shapes in edge portions of a fluorescent material layer, a bulb for such a color cathode ray tube and methods for the production thereof.
The method for producing a bulb for a color cathode ray tube, provided by the present invention, is a method for producing a bulb for a color cathode ray tube, said bulb comprising a face plate and a color selection member having a plurality of opening portions, and satisfying the following expression (1), wherein X is a nominal diagonal inchage of the bulb and P (unit: mm) is a pitch of the opening portions along an electron beam sweep direction in the central portion of the bulb.
Further, the method for producing a color cathode ray tube, provided by the present invention, is a method for producing a color cathode ray tube constituted of a bulb for a color cathode ray tube, said bulb comprising a face plate and a color selection member having a plurality of opening portions, and said bulb satisfying the following expression (1), wherein X is a nominal diagonal inchage of the bulb and P (unit: mm) is a pitch of the opening portions along an electron beam sweep direction in the central portion of the bulb.
In a circumferential portion of the face plate along the electron beam sweep direction, it is not necessary to satisfy the following expression (1).
0.0117Xxe2x88x920.0457 less than P less than 0.018Xxe2x88x920.0771xe2x80x83xe2x80x83(1) 
The above methods includes the step of exposing a light, sensitive film formed on an inner surface of the face plate on the basis of a transmitted-light strength distribution of superposed Fresnel diffraction waves of exposure lights which are emitted from a plurality of exposure light sources arranged in different positions along the electron beam sweep direction and pass through the opening portions formed in the color selection member, to form exposed regions in the light sensitive film which regions correspond to the opening portions,
in which a transmitted-light strength of superposed Fresnel diffraction waves of the two exposure lights (to be sometimes referred to as xe2x80x9csuperposed transmitted-light strengthxe2x80x9d hereinafter), out of a plurality of the exposure lights, which are emitted from the two exposure light sources contributing to the exposure of edge portions of the light sensitive film corresponding to each opening portion satisfies the following requirements (A) and (B);
(A) in an area of the superposed transmitted-light strength in which area the superposed transmitted-light strength on the light sensitive film decreases along the electron beam sweep direction (x direction) from a central portion of the exposed region of the light sensitive film corresponding to each opening portion, the derivative of the first order (∂i/∂x) of the superposed transmitted-light strength has at least one upward-convex area, and
(B) the edge portions of the exposed light sensitive film corresponding to each opening portion are included in an area of the superposed transmitted-light strength which area corresponds to the upward-convex area which appears first along the electron beam sweep direction (x direction) from the central portion of the exposed region corresponding to each opening portion, out of the upward-convex areas of the derivative of the first order (∂i/∂x) of the superposed transmitted-light strength.
The above xe2x80x9ctwo exposure lights which are emitted from the two exposure light sources contributing to the exposure of edge portions of the light sensitive film corresponding to each opening portionxe2x80x9d means the following. When the exposure light sources are individually operated to expose the light sensitive film formed on the inner surface of the face plate, each of the above exposure lights is an exposure light which satisfies IMINxe2x89xa6I1 wherein I1 is a transmitted-light strength in the edge portion of the light sensitive film corresponding to each opening portion and IMIN is a lowest transmitted-light strength required for exposure of the light sensitive film.
Of upward-convex areas of the derivative of the first order (∂I/∂x) of the above superposed transmitted-light strength, the upward-convex area which appears first along the electron beam sweep direction from the central portion of the exposed region will be referred to as a first wave, and the upward-convex area which appears thereafter will be referred to as a second wave, for the convenience.
In the method for producing a bulb for a color cathode ray tube or the method for producing a color cathode ray tube, provided by the present invention (these methods will be sometimes generally referred to as xe2x80x9cmethod of the present inventionxe2x80x9d hereinafter), preferably, the following expression (2) is satisfied. In the expression (2), GH (unit: mm) is a distance between the inner surface of the face plate and the color selection member in the central portion of the bulb and LT (corresponding to a so-called opening rate) is a value obtained by dividing a size (unit: mm) of the opening portion along the electron beam sweep direction in the central portion of the bulb by the pitch P (unit: mm). In a circumferential portion of the face plate along the electron beam sweep direction, it is not required to satisfy the following expression (2).
2.8xc3x9710xe2x88x922 less than Pxc3x97LTxc3x97GHxe2x88x92xc2xd less than 4.1xc3x9710xe2x88x922xe2x80x83xe2x80x83(2) 
After the formation of the exposed regions in the light sensitive film formed on the inner surface of the face plate which regions correspond to the openings, the method of the present invention may further includes the steps of selectively removing the light sensitive film by development, forming a light-absorption layer (for example, black-matrix) on the exposed inner surface of the face plate and removing the remaining portion of the light sensitive film, and then, forming a fluorescent material layer on the exposed inner surface of the face plate. For reliably forming the exposed regions having a proper size, preferably, a correction lens system is disposed between the exposure light sources and the color selection member. In the method for producing a bulb for a color cathode ray tube, provided by the present invention, the face plate and a funnel, etc., are assembled to complete the bulb for a color cathode ray tube. In the method for producing a color cathode ray tube, provided by the present invention, an electron gun is incorporated into the obtained bulb for a color cathode ray tube, and the inside of the bulb is vacuumed, to complete the color cathode ray tube.
The method of the present invention may employ a constitution in which the number of the exposure light sources is 2. In this case, the two exposure light sources correspond to xe2x80x9cthe two exposure light sources contributing to the exposure of edge portions of the light sensitive film corresponding to each opening portionxe2x80x9d. There may be also employed a constitution in which the number of the exposure light sources is 3 or more and the transmitted-light strength of superposed Fresnel diffraction waves of the exposure lights from all of the exposure light sources satisfies ICENTER/IEDGExe2x89xa71.2, wherein ICENTER is a transmitted-light strength in the central portion of the exposed region corresponding to each opening portion and IEDGE is a transmitted-light strength in the edge portion of the light sensitive film corresponding to each opening portion. In the above constitution, reliable exposure is secured particularly in the central portion of the light sensitive film corresponding to each opening portion. In this case, two exposure light sources out of the three or more exposure light sources correspond to xe2x80x9cthe two exposure light sources contributing to the exposure of edge portions of the light sensitive film corresponding to each opening portionxe2x80x9d, and the remaining exposure light source or sources contribute, for example, to the exposure of the central portion of the exposed region corresponding to each opening portion. When three or more exposure light sources are used, preferably, the remaining exposure light source or sources (to be sometimes referred to as xe2x80x9cexposure light source for exposing a central portionxe2x80x9d hereinafter) are disposed between the two exposure light sources contributing to the edge portion of the light sensitive film corresponding to each opening portion (to be sometimes referred to as xe2x80x9cexposure light source for exposing an edge portionxe2x80x9d hereinafter). However, the light source or sources for exposing a central portion may be disposed outside the two exposure light sources for exposing an edge portion. Further, when four or more exposure light sources are used, preferably, the exposure light sources for exposing a central portion are disposed between the two exposure light sources for exposing an edge portion. Alternatively, the exposure light sources for exposing a central portion may be disposed outside the two exposure light sources for exposing an edge portion, or the exposure light sources for exposing a central portion may be disposed between and outside the two exposure light sources for exposing an edge portion. Each exposure light source may be constituted, for example, of an ultraviolet light source.
The bulb for a color cathode ray tube provided by the present invention for achieving the above object is a bulb comprising a face plate and a color selection member having a plurality of opening portions.
The color cathode ray tube of the present invention for achieving the above object is a color cathode ray tube constituted of a bulb for a cathode ray tube, said bulb comprising a face plate and a color selection member having a plurality of opening portions.
The bulb for a color cathode ray tube or the color cathode ray tube provided by the present invention satisfies the following expressions (1) and (2), wherein X is a nominal diagonal inchage of the bulb, P (unit: mm) is a pitch of the opening portions along an electron beam sweep direction in the central portion of the bulb, GH (unit: mm) is a distance between an inner surface of the face plate and the color selection member in the central portion of the bulb, and LT (corresponding to a so-called opening rate) is a value obtained by dividing a size (unit: mm) of the opening portion along the electron beam sweep direction in the central portion of the bulb by the pitch P (unit: mm).
0.0117Xxe2x88x920.0457 less than P less than 0.018Xxe2x88x920.0771xe2x80x83xe2x80x83(1) 
2.8xc3x9710xe2x88x922 less than Pxc3x97LTxc3x97GHxe2x88x92xc2xd less than 4.1xc3x9710xe2x88x922xe2x80x83xe2x80x83(2) 
In a circumferential portion of the face place along the electron beam sweep direction, it is not required to satisfy the above expressions (1) and (2).
The pitch of the opening portions may be constant toward the circumferential portion of the face plate along the electron beam sweep direction. Alternatively, the above pitch may be broadened toward the circumferential portion along the electron beam sweep direction, whereby the color purity in the circumferential portion of the color cathode ray tube can be improved to a great extent. The size of the opening portions may be constant toward the circumferential portion along the electron beam sweep direction or may be broadened toward the circumferential portion along the electron beam sweep direction.
The edge portion of the exposed light sensitive film is included in the area of the superposed transmitted-light strength which area corresponds to the first wave of the derivative of the first order (∂I/∂x). However, it is not much desirable that the edge portion of the exposed light sensitive film is included in the area of the superposed transmitted-light strength which area corresponds to the first wave near a transition area from the first wave to the second wave of the derivative of the first order (∂I/∂x). Therefore, preferably, the following xcex1, xcex2 and xcex3 satisfy the following expression (3), wherein xcex1 is a peak value of the first wave of the derivative of the first order (∂I/∂x), xcex2 is a value of the derivative of the first order (∂i/∂x) in the transition area from the first wave to the second wave, and xcex3 is a value of the derivative of the first order (∂i/∂x) in the area (portion) of the superposed transmitted-light strength in which the edge portion of the exposed light sensitive film is included.
xcex3xe2x89xa7xcex2+0.1(xcex1xe2x88x92xcex2)xe2x80x83xe2x80x83(3) 
FIGS. 49A and 49B show layouts of the color selection member and the fluorescent material layers when the color selection member is of aperture grille type. FIG. 49A also shows the pitch P of the opening portions along the electron beam sweep direction in the central portion of the bulb. In the color selection member of aperture grille type, a plurality of slits corresponding to the opening portions are arranged in parallel. The pitch P corresponds to a distance from the center of one slit to the center of a neighboring slit.
FIGS. 50A and 50B show layouts of the color selection member and the fluorescent material layers when the color selection member is of dot-type shadow mask type. FIG. 50A also shows the pitch P of the opening portions along the electron beam sweep direction in the central portion of the bulb. In the color selection member of dot-type shadow mask type, a plurality of circular through holes corresponding to the opening portions are arranged in apexes of triangles. The pitch P corresponds to a distance from the center of one through hole to the center of a neighboring through hole along the electron beam sweep direction.
FIGS. 51A and 51B show layouts of the color selection member and the fluorescent material layers when the color selection member is of slot-type shadow mask type. FIG. 51A also shows the pitch P of the opening portions along the electron beam sweep direction in the central portion of the bulb. In the color selection member of slot-type shadow mask type, a plurality of short slits corresponding to the opening portions are arranged in one direction (at right angles with the electron beam sweep direction), and these slits are arranged in parallel with one another. The pitch P corresponds to a distance from the center of one short slot to the center of a neighboring short slot along the electron beam sweep direction.
In FIGS. 49B, 50B and 51B, symbols xe2x80x9cRxe2x80x9d, xe2x80x9cGxe2x80x9d and xe2x80x9cBxe2x80x9d stand for a fluorescent material layer for emitting a light in red, a fluorescent material layer for emitting a light in green and a fluorescent material layer for emitting a light in blue, respectively. In FIGS. 49A and 49B, the opening portions and the fluorescent material layers are provided with slanting lines for clarification thereof.
The face plate may have a lateral dimension:vertical dimension ratio of nominal 16:9 or 4:3. Although not specially limited, the structure of the face plate includes a structure in which the outer surface of effective screen field of the face plate may be spherical or curved, a structure in which the outer surface of the effective screen field of the face plate is substantially flat and the thickness of the circumferential portions of the effective screen filed in the horizontal direction is larger than the thickness of the central portion of the effective screen field, and a structure in which the face plate in the effective screen field has a substantially uniform thickness. The structure of the color cathode ray tube includes a structure having a bulb for a color cathode ray tube in which the outer surface of the effective screen field of the face plate is substantially flat and a color selection member which is disposed to face the inner surface of the face plate inside the bulb and has a convex curvature toward the face plate. In this case, there may be employed a constitution in which the inner surface of the face plate has a concave curvature toward the color selection member and the curvature of the color selection member is greater than the curvature of the inner surface of the face plate or a constitution in which the inner surface of the face plate has a concave curvature toward the color selection member and the curvature of the color selection member is nearly equal to the curvature of the inner surface of the face plate. However, the above members shall not be limited to the above structures or constitutions. The above effective screen field refers to a face plate region where images are actually displayed when the bulb is incorporated into the color cathode ray tube. That the effective screen field of the face plate is substantially flat means that the effective screen field is flat within the production tolerance of the face plate. For example, in the face plate for a 28-inch bulb in which X=28, the production tolerance is approximately 1 to 2 mm or less. In the above case, the effective screen field appears to be substantially completely flat when visually observed. Further, a change in the thickness of the effective screen field from the central portion of the effective screen field to the circumferential portions in the horizontal direction can be expressed by an arc or a multinomial. When it is assumed that the bulb for a color cathode ray tube is held in a horizontal position and that the face plate is cut with a vertical plane, the curve drawn by the inner surface of the face plate may be a straight line, an arc, or a curve expressed by a multinomial. If the circumferential portions of the effective screen field in the horizontal direction has a thickness T and if the central portion of the effective screen field has a thickness of To, preferably, T=1.2T0 to 1.3T0. The curvature of the inner surface of the face plate and the curvature of the color selection member refer to average values of curvatures of curves drawn by the cross section of the inner surface of the face plate and the cross section of the color selection member when it is assumed that the bulb is held in a horizontal position and that the face plate and the color selection member are cut with a horizontal plane. The above curves are preferably of an arc. In these cases, the curvature of the inner surface of the face plate and the curvature of the color selection member correspond to reciprocals of radii of the above arcs.
The material for constituting the light sensitive film includes, for example, PVP (polyvinyl pyrrolidone) and PVA (polyvinyl alcohol).
In designing the bulb for a color cathode ray tube or the color cathode ray tube, parameters such as the pitch of the opening portions and the size of the opening portions can be determined with a freedom to some extent although a certain limitation is imposed thereon. In the method of the present invention, the above expression (1) is satisfied and the edge portions of the exposed light sensitive film are included in the area of the superposed transmitted-light strength which area corresponds to the first wave in the derivative of the first order of the superposed transmitted-light strength, so that the edge portions of the light sensitive film remaining after exposure and development have no convexo-concave shapes. In the bulb for a color cathode ray tube or the color cathode ray tube provided by the present invention, the above expressions (1) and (2) are satisfied, so that the edge portions of the fluorescent material layer have no convexo-concave shapes.